Field of Disclosure
The present disclosure relates to a wind power generation system. More particularly, the present disclosure relates to a doubly-fed wind power generation system.
Description of Related Art
In recent years, the wind power generation technology uses the electronic converter (such as the alternating-current/direct-current/alternating-current converter in combination with a high level control system) such that the grid frequency and the mechanical rotor frequency can be decoupled. The wind power generator module can therefore be operated under variable speed. As a result, the improvement of the variable speed wind power generator module is obvious in recent years.
Mega-watts wind power generation systems can be categorized into full power wind power generation systems and doubly-fed wind power generation systems. The full power wind power generation systems mainly include the full power wind power generator modules having a full power generator and full power converters. Reference now made to FIG. 1, FIG. 1 is a diagram of a conventional full power wind power generation system 100. The full power wind power generation system 100 includes a fan 110, a full power generator 120, a generator-side converter 130, a grid-side converter 140 and a direct current (DC) bus 150. The fan 110 is coupled to the full power generator 120. A stator winding 121 of the full power generator 120 is coupled to the generator-side converter 130 through a switch SW1. The generator-side converter 130 and the grid-side converter 140 use the same DC bus 150. The grid-side converter 140 is coupled to the grid 160 through a switch SW2.
By using paddles 111, the fan 110 converts the wind energy to a mechanical torque (rotational inertia of paddles). The full power generator 120 converts the mechanical torque to the electric energy. The electric energy outputted by the full power generator 120 is transmitted to the grid 160 through the conversion of the generator-side converter 130 and the grid-side converter 140. In the full power wind power generation system 100, the generator-side converter 130 and the grid-side converter 140 are full power converters. In other words, the generator-side converter 130 and the grid-side converter 140 process all the outputted power. The full power generator 120 can be a permanent-magnet synchronous generator, an electric excitation generator or an induction generator and so on. In another conventional embodiment, the fan 100 can be coupled to the generator 120 through a gear box (not illustrated). The gear box can turn a low rotation speed of the paddles to a high rotation speed of the generator.
The advantages of the full power generator modules include wide operation range of power generation, low cut-in wind speed and great adaptability to the grid. However, since the cost of the full power generator and the full power converter is high (the generator-side converter 130 and the grid-side converter 140 use the converter of large capacity), the manufacturing cost of the full power generator module is high.
Besides, the doubly-fed wind power generation systems mainly include doubly-fed wind power generation modules that have a doubly-fed induction generator and doubly-fed converters. The advantage of the doubly-fed wind power generation modules includes the low cost of the equipments that is much lower than that of the full power generator modules. However, the disadvantage of the doubly-fed wind power generation modules includes the low efficiency of the power generation under a low wind speed, a greater loss under the low rotation speed and the limited voltage endurance of the electronic components in the converters due to the range of the rotation speed of the generator that results in a limited operation range.
Accordingly, what is needed is a wind power generation system that has a high efficiency and a high cost-performance.